Steam generating unit



Oct. 30, 1962 N. s. BLODGETT 3, 0

STEAM GENERATING UNIT Filed July 27, 1961 5 Sheets-Sheet 1 NORMAN 5.BLODGETT INVENTOR.

A TTOR/VE Y 0a. 30, 1962 N. s. BLODGETT 3,060,907

STEAM GENERATING UNIT Filed July 27, 1961 3 Sheets-Sheet 2 FIG. 2.

. A z NORMA s. DGETT INVENT OR BYM X TTORNEY Oct. 30, 1962 N. s.BLODGETT 3,060,907

STEAM GENERATING UNIT Filed July 27, 1961 3 Sheets-Sheet 3 FIG. 3.

I 4 1 v 1 1 1 1 a o a I 1 I 1 o 1 s. INVENT OR United States Patent3,665,587 STEAM GENERATNG UNIT Norman S. Blodgett, Westhero, Mass,assignor to Riley Stoker Corporation, Worcester, Mass a corporation ofMassachusetts Filed July 27, 1961, Ser. No. 127,226 4 Claims. (Cl.122-479) This invention relates to a steam generating unit and moreparticularly to apparatus arranged to generate steam and to regulate thetemperature of superheated steam which is produced therein.

There have been many methods suggested in the past for maintaining thetemperature of the superheated steam in a steam generating unit at afixed value, irrespective of changes in load on the unit. Among thesemethods is that of by-passing portions of the gas away from sections ofsuperheater heat exchange surface. Also, there is the method in whichthe temperature of the gases passing over convective superheaters isregulated by regulating the residence time of the gases in the maincombustion chamber by the use of tilting burners. There is the method ofsuperheat control by gas recirculation in which gases from the backpasses are returned in regulated amounts to the main combustion chamberto increase or decrease the mass flow of gases over convectionsuperheater units. Of course, there is also the old method ofdesuperheating the superheated steam by injecting a spray of water intoit. Another method of controlling superheat is described in the patentto Miller No. 2,947,289, in which the flame rising vertically throughthe furnace is moved to various positions between the front wall and therear wall in order to regulate superheat. There are some boilerconditions under which this last method of controlling superheat doesnot give a suincient range of superheat temperature change. While it istrue that this method can be combined with desuperheating methods andwith -by-pass methods of superheat control to give suflicient range,these last two methods tend to affect the overall efiiciency of theboiler. These deficiencies in the prior art have been obviated by thepresent invention in a novel manner.

It is, therefore, an outstanding object of the present invention toprovide a steam generating unit having apparatus for the control ofsuperheat in which the heat discarded from the cycle at certain loads isreduced to a minimum value.

Another object of the invention is the provision of an apparatus for thecontrol of superheat whose action is not detrimental to the overalloperation of the steam generating unit.

Another object of the invention is the provision of an apparatus for thecontrol of superheat which makes use of the flame-positioning method andin which the range of control has been greatly increased.

With these and other objects in view, as will be apparent to thoseskilled in the art, the invention resides in the combination of partsset forth in the specification and covered by the claims appendedhereto.

The character of the invention, however, may be best understood byreference to one of its structural forms, as illustrated by theaccompanying drawings in which:

FIG. 1 is a vertical sectional view of a steam generating unit embodyingthe principles of the present invention,

FIG. 2 is a schematic view of the unit to show its operation at lowload, and

FIG. 3 is a similar schematic view of the unit taken during high loadoperation.

In the specification which follows, the expressions longitudinal,transverse refer to those directions as applied to a steam generatingunit in the ordinary practice 3,5653%? Patented Oct. 30, 1962 in thatart and in general refer to the flow of gas through the unit.

Referring first to FIG. 1, wherein are best shown the general featuresof the invention, the steam generating unit, indicated generally by thereference numeral 11, is shown as consisting of a furnace 12 and aboiler 13 mounted on a supporting structure 14. The furnace 12 consistsof a front wall 15 and a rear wall 16 which, with side walls 17, definea vertically-elongated combustion chamber 18. Underlying the combustionchamber is a slag basin 19 formed of refractory material. The front wall15 is provided with a nose 21 located in its lower portion directlyoverlying the slag basin 19 and provided on its downwardly-directedsurface with a burner 22. A similar nose 23 is provided in the rear Wall16 and a burner 24 is mounted on the downwardly-directed surface of thatnose.

The boiler 13 consists of an upper steam-and-water drum 25 joined bydowncomer tubes 26 to a lower drum 27, both drums extending transverselyfo the unit. Large downcomer tubes 28 extend from the lower drum 27 to aheader 29 extending around the periphery of the slag basin 19.Water-wall tubes 31 extend upwardly from the header 29 along the frontwall 15, the rear wall 16, and the side walls 17. These water-wall tubesare connected at the upper part of the furnace to the steam-andwaterdrum 25. Alternate water-wall tubes on the back wall 16 are formed withforward loops 32 as will be described more fully hereinafter. Thesetubes serve to define an upper pass 34- between their forwardlyprojecting portions and the roof 35 of the furnace. A refractory wall 36extends downwardly from the steam-andwater drum 25 and serves to dividethe rearward portion of the unit into back passes 37 and 38. A duct 39leads from the back pass 38 to a dust collector 41 which, in turn, isconnected in the conventional manner through a rotary regenerative airheater, an induced draft fan and a breaching to a stack, all not shown.

The forced draft fan is connected through the air heater to a duct 46having branch ducts 47 and 48 leading to the burners 24 and 22,respectively. A duct 49 leads from the duct 46 to an attrition-typepulverizer (not shown). Pipes 53 lead from the output of the pulverizerto the burners 22 and 24.

As is evident in FIG. 1, the steam-and-water drum 25 is provided with asteam separator of the usual type. Tubes 54 lead from the upper part ofthe steam-and-water drum to a header 55 arranged beside the front wall15 of the furnace. Below the header 55 is arranged another header 56 ofa similar type. Joining these headers and lying within the furnaceagainst the forward wall 15 is a radiant superheater 57. Tubes 58 leadfrom the header 56 to a header 59 which is connected through aconvection superheater 61 lying in the pass 37 to a convectionsuperheater 62 lying in the upper pass 34. The output end of thesuperheater 62 is connected to superheater platens 63 hanging downwardlyfrom the roof 35 into a restricted passage 33 between the forward wall15 and the foremost portion of the tube loops 3-2. The output of theplaten 63 is connected to a superheated steam header 64 which, in turn,is connected by a high pressure pipe 65 to the high-pressure section ofthe turbine (not shown).

The output of the high pressure section of the turbine is connected bymeans of a pipe 66 to a header 67 arranged adjacent the rear wall 16 ofthe furnace. A similar header 68 is mounted above the header 67 andthetwo are joined by a radiant reheater 69 which lies closely adjacentthe inner surface of the rear wall. The header 68 is connected by a pipe71 to an input header 72 connected to one end of a convection reheater73 lying in a the upper pass 34 between the superheater 62 and thesuperheater platen 63. The output of the reheater 73 is connected to areheater steam header 74 which, in turn, is connected by means of ahigh-pressure pipe 75 to the low pressure section of the turbine. Theburners 22 and 24 are similar to those described in Patent No.2,947,289. For instance, in the case of the burner 22, the air duct 48is connected to a burner housing. Centrally of the housing is located acontinuous spark igniter (not shown) and a gun 78 for intrd-oucingpulverized coal into the burner. The conduit 53 leading from thepulverizer 51 is connected to the gun and in the central part of the gunis a gas gun to insure ignition. The water-wall tubes 31 are bentrearwardly in the vicinity of the burner 22 to form passages for theflow of fuel and air. At the mouth of the burner below the gun 78 arelocated pivoted vanes 83 which are connected through a mechanicallinkage to an actuating rod 84. In the upper part of the burner arelocated pivoted vanes 85 which are connected through a mechanicallinkage to an actuating rod 86. The burner 24 is similarly provided witha fuel gun 87, lower vanes 88 whose angularity is adjustable by means ofan actuating rod 89, and upper pivoted vanes 91 whose angularity isadjustable by means of an actuating rod 89, and upper pivoted vanes 91Whose angularity is adjustable by means of an actuating rod 92.

The actuating rod 86 for the vanes 85 is connected to the piston rod ofa hydraulic linear actuator 96, while the actuating rod 92 of the vanes91 is connected to a similar actuator 97. The actuator 96 is connectedby conduits 98 and 99 to a controller 101 and the linear actuator 97 isconnected to the controller by means of conduits 102 and 103. The airduct 48 leading to the burner 22 is provided with a control damper 104which is connected for pivotal action through a mechanical linkage tothe piston rod of a linear actuator 105 Whose piston is movable underthe control of conduits 106 and 107 by which it is connected to thecontroller 101. In a similar manner, the duct 47 leading to the burner24 is provided with a pivoted damper 108 which is connected through alinkage mechanism to the piston rod of a linear actuator 109. Thisactuator is connected to the controller 101 by means of conduits 111 and112. The superheated steam header 64 has mounted therein atemperature-indicating device 113 of the usual type, and this device isconnected through a line 114 to the controller 101. A similartemperature-measuring device 115 resides in the reheated steam header 74and is connected by a line 116 to the controller 101. The controller 101is of the usual type used in temperature control applications; itconsists of an apparatus which is well known in the art for convertingelectrical signals in the lines 114 and 116 into hydraulic flow throughthe lines 106, 107-, 98, 99, 111, 112, 102, and 103 leading to thevarious hydraulic linear actuators associated with the apparatus; sincethe controller is not part of the present invention in its detailedform, it is not felt that a specific descripion thereof is not necessaryadequately to describe the present invention.

As has been stated, each of the alternate tubes in the rear water-walltubes of the wall 16 of the furnace has been bent forwardly to form aloop 32 which resides above the combustion chamber. Each tube is bent atan angle of approximately 45 to the vertical to provide a portion 117extending forwardly from a position well above the lower drum 27 of theboiler. Each tube is then given a return bend to return to verticalalong with the other tubes which were not provided with a loop. Theloops extend to a position somewhat forwardly of the midpoint betweenthe front and rear wall of the furnace. Mounted on the loops 32 arerefractory blocks 121 forming a nose 122. The refractory blocks extendalong the inclined portions 117 of the loops 32, along the returninclination and along the back wall to define a chamber 123 within thenose. The refractory blocks are omitted from a portion of the portion117 somewhat forwardly of the rear wall 16 to provide an opening 124.Between the forward edge of the nose and the front wall is located thepassage 33 leading to the upper pass 34. The convection superheater 62is located entirely above the nose 122. At the same time, the convectionreheater 73 is located above the nose at the forward portion of it and aportion of the reheater extends for- Wardly of the forward edge of thenose. The superheater platens 63 lie entirely within the passage 33forwardly of the nose. The refractory blocks 121 fit tightly around thetubes and are bonded together by cement in the usual manner to provide agas-tight baffie construction.

The interior of the chamber 123 is entirely vacant except, of course,for certain structural elements for supporting the nose and therefractory. Entering the chamher through one of the side walls 17 is anopening 125 formed by bending the tubes laterally in a well-knownmanner. Attached to this opening is a recirculated gas duct 126 whichextends around the boiler on the exterior thereof and is attached at itsother end to an opening 127 in the duct 39. The intermediate portion ofthe duct 126 is provided with regulating dampers 128 which are connectedthrough suitable linkages to the piston rod of a hydraulic linearactuator 129. The actuator is connected by conduits 131 and 132 to thecontroller 101.

The operation of the apparatus will now be readily understood in view ofthe above description. The furnace 12 and the boiler 13 operate in theusual manner. Because of the restricted nature of the bottom of thecombustion chamber 18 below the level of the noses 21 and 23, it is veryhot and quite complete combustion takes place in this high-temperaturecell. The gases passing upwardly in the restricted zone between thenoses 21 and 23 form a flame 120 which may be manipulated so as to flowclose to the front wall 15, close to the rear wall 16, or to flow in anyposition intermediate of the walls. In the sense of flame, the applicantmeans the line of greatest mass flow and highest gas temperature whichis usually indicated in a furnace as a flame; this flame may or may notbe luminous, depending upon various factors such as the nature of thefuel and the completeness of combustion. The fiame may be manipulated ina manner described in the above-identified patent of Miller by adjustingthe angles of the vanes in the burners through the linear actuators 96and 97 or by adjusting the air-flow through the burners by means of theactuators and 109 which manipulate the dampers 104 and 108.

Referring now to FIGS. 2 and 3, it is evident that the position of theflame is manipulated by changing the angularity of the vanes in'theburners. In FIG. 2, which shows the relationships at low load, the flameis shown as rising close to the front wall 15. The flame 120 passesdirectly along the front wall 15 and through the passage 33 close to thefront wall. From there, the gas flow is directed under the roof 35through the upper pass 34. In the process of doing this, these gasespass over the superheater platens 63, the convection reheater 73, andthe convection superheater 62; the gases eventually pass through the gasoiftake leading from the furnace into the backpasses. Because the flameextends upwardly along the front part of the furnace, a zone of reducedpressure is created under the nose and the flow of recirculated gasestakes place from the opening 124 downwardly well into the furnace wherethey mix with the gases rising along the front wall. Now, it is wellknown that uncorrected superheat tends to be low at low loads because ofthe rising character of a convection superheat curve. In the presentcase, the flame 124 and the greatest mass of gases pass by the mostdirect path from the burners to the convection sections of superheater.This means that they reach these superheaters at the highest temperaturebecause there has been the least possibility of heat radiation to thewalls of the furnace to cool the gases. This gives a tendency to ahigher superheat temperature. Furthermore, the flame is closer toradiant superheater sections 57 and the superheater platens 63 whichabsorb considerable heat by radiation from the combustion chamber.Furthermore, the gases which flow from the opening 124 downwardlythrough the furnace to mix with the gases from the burners to passupwardly once more through the forward pass 33 constitute a form of gasrecirculation which increases the mass flow of gases over the convectionsuperheater surfaces, thus raising the temperature of steam in thesuperheaters. This recirculation of gases takes place automatically byregulation by the controller 101 which acts through the conduits 131 and132 and the actuator 128 to increase the amount of gas recirculated atlow load.

Referring to FIG. 3 which shows the relationships which exist at highload, the flame 120 is shown as being positioned close to the rear wall16, so that a large percentage of the gases have a tendency to godirectly around the nose and through the gas oiftake to the backpass 37.The controller 101 is set at high load to regulate the dampers 128 sothat only a small of gas is recirculated. The gases from the burnerspass over the underside of the nose and pick up the recirculated gasfrom the opening 124. The combination of the lower quantity ofrecirculated gas and the flame up the back wall has a tendency to lowerthe temperature of superheat. First of all, there is littlerecirculation downwardly through opening 124 as was provided at lowload. Secondly, those gases which pass over the convection superheater62 have reached this area by a longer path, since they are forced tofirst pass along the rear wall of the furnace and then move forwardly inthe furnace so that their residence time in the furnace is longer (andtheir temperature when they reach the convection superheater is lower).Furthermore, the flow of gases over the convection units is smaller inamount; that is to say, the mass flow over the convection superheater isless. Also, with the flame at the rear of the furnace, the radiation tothe radiant superheater 5'7 and the radiant parts of the superheaterplaten 63 is less. All of these factors have a tendency to maintainsuperheat at a predetermined value, despite the normal tendency forsuperheat to be high at high load. At intermediate loads, of course, themovement of the flame to positions between the front and rear walls willproduce variations of these factors and will permit close regulation ofsuperheat temperature.

An examination of FIGS. 2 and 3 shows the decided benefits of combiningthe flameapositioning control with the introduction of recirculated gasthrough the lower surface of the nose. At low load, as shown in FIG. 2,the suction produced by the flame going up the front wall causes therecirculated gas to be projected downwardly into the furnace aconsiderable distance before turning to meet the main flame. Now, at lowload a large amount of recirculated gases is used and it is importantthat the recirculated gases and the main burner gases be thoroughlymixed before they arrive at the convection surfaces. By starting themixing and introduction well down in the furnace, as will take placewith the present construction, many of the disadvantages of gasrecirculation control and of flame-positioning control are obviated. Atthe same time, when the apparatus is operated at high load, as shown inFIG. 3, the movement of the flame up the back wall means that verythorough mixing still takes place between the burner gases and therecirculated gases; at high load, of course, only a small amount ofrecirculated gases is used, but, neverthless, it is important that thesegases be thoroughly mixed with the gases coming from the burner. Now,with the present apparatus, the main burner gases wipe over the lowersurface of the nose and over the opening 124, thus producing a verythorough mixing. Since the velocity of the recirculated gases is verylow and the recirculated gases do not have enough energy normally toproduce good mixing, this is an important feature. Without thisarrangement the recirculated gases would have a tendency to passupwardly along the nose and form a striation of low temperature gasesalong the nose which would result in temperature difficulties in theconvection superheater.

It is obvious that minor changes may be made in the form andconstruction of the invention without departing from the material spiritthereof. It is not, however, desired to confine the invention to theexact form here-in shown and described, but it is desired to include allsuch as properly come within the scope claimed.

The invention having been thus described, What is claimed as new anddesired to secure by Letters Patent, is:

1. A steam generating unit, comprising a vertically elongated combustionchamber having front, rear, and side walls, a radiant superheaterassociated with the front wall and a radiant reheater associated withthe rear wall, opposed abutments extending from the front and rear Wallsand defining a high-temperature cell located at the bottom of thecombustion chamber, directional-flame burners mounted on the under sidesof the abutment for producing a mass of hot products of combustion, agasoiftake at the upper part of the rear wall, a nose extending acrossthe combustion chamber immediately below the gas off-take, a convectionsuperheater overlying the nose, the nose having a recirculated gaschamber therein and having an inclined undersurface on which therecirculated gas chamber opens, a back pass into which the gases flowafter passing over the convection superheater, a recirculated gas ductconnecting the gas chamber to the back pass, dampers located in the ductautomatically adjusted in response to superheat temperature to causelarge amounts of gas to flow to the gas chamber at low load and smallamounts at high load, and positioning means associated with thedirectional-flame burners tolocate the line of greatest mass flow at adesired position between the front and rear walls, the said meanscausing the flame to be located from a position adjacent the rear wallat high load to a position adjacent the front wall at low load to aid inmaintaining the temperature of superheated steam at a predeterminedvalue.

2. A steam generating unit, comprising a verticallyelongated combustionchamber having front, rear, and side walls, a radiant superheaterassociated with one wall, opposed abutments extending from opposed wallsand defining a high-temperature cell located at the bottom of thecombustion chamber, directional-flame burners mounted on the undersidesof the abutments for producing a mass of hot products of combustion, agas-ofitake at the upper part of the wall opposite the said one wall, anose extending across the combustion chamber immediately below the gasoff-take, a convection superheater overlying the nose, the nose having arecirculated gas chamber therein and having an inclined undersurface onwhich the recirculated gas chamber opens, a back pass into which thegases flow after passing over the convection superheater, a recirculatedgas duct connecting the gas chamber to the back pass, dampers located inthe duct automatically adjusted in response to superheat temperature tocause large amounts of gas to flow to the gas chamber at low load andsmall amounts at high load, and positioning means associated with thedirectional-flame burners to locate the line of greatest mass flow at adesired position between the said one wall and the said opposite wall,the said means causing the flame to be located from a position adjacentthe said one wall at high load to a position adjacent th said oppositewall at low load to aid in maintaining the temperature of superheatedsteam at a predetermined value.

3. A steam generating unit, comprising a verticallyelongated combustionchamber having front, rear, and side walls, a radiant superheaterassociated with the front wall and a radiant reheater associated withthe rear wall, opposed abutments extending from the front and rear wallsand entirely across the chamber from side wall to side Wall to define ahigh-temperature cell located at the bottom of the combustion chamber,intertube, adjustable-vane directional-flame burners mounted on theundersides of the abutments for producing a mass of hot products of com'bustion, a gas-oiftake at the upper part of the rear wall, a noseconsisting of refractory mounted on water wall tubes extending acrossthe combustion chamber immediately below the gas elf-take, a convectionsuperheater overlying the nose, the nose having a recirculated gaschamber therein and having an inclined undersurface on which opens apassage between the tubes into the recirculated gas chamber, a back passinto which the gases flow after passing over the convection superheater,a recirculated gas duct connecting the gas chamber to the back pass, amain control receiving signals indicative of the temperature of steamleaving the superheater, of the temperature of steam leaving thereheater, and of load on the unit, dampers located in the ductautomatically adjusted by the main control in response to superheattemperature to cause large amounts of gas to flow to the gas chamber atlow load and small amounts at high load, and positioning means connectedto the main control and associated with the directional-flame burners tolocate the line of greatest mass flow at a desired position between thefront and rear walls, the said means causing the flame to be locatedfrom a position adjacent the rear Wall at high load to a positionadjacent the front wall at low load to aid in maintaining thetemperature of superheated steam at a pre-determined value.

4. A steam generating unit, comprising (a) front, rear, bottom, and sidewalls defining a vertically-elongated combustion chamber,

(b) a radiant superheater associated with the upper portion of one wall,

(c) at least one abutment extending across the chamber adjacent thebottom wall and defining with the bottom wall a high-temperature celllocated at the lower end of the combustion chamber,

(d) directional-flame burners mounted on the underside of the abutmentfor producing a mass of hot products of combustion,

(e) a gas oil-take at the upper end of the combustion chamber,

(f) a gas recirculation opening at the upper portion of a wall oppositethe said one wall,

g) a back pass into which the gases flow after passing through the gasofi-take,

(h) a recirculated gas duct connecting the back pass to the saidopening,

(i) a main control receiving signals indicative of the temperature ofsteam leaving the superheater and of load on the unit,

(j) dampers located in the duct automatically adjusted by the maincontrol to cause large amounts of gas to flow to the opening at low loadand small amounts at high load,

(k) a convection superheater located in the said back pass,

(I) and positioning means connected to the main control and associatedwith the directional-flame burners to locate the line of greatest massflow at a desired position between the said one wall and the saidopposite Wall, the said means causing the flame to be located from aposition adjacent the said opposite wall at high load to a positionadjacent the said one wall at low load to aid in maintaining thetemperature of superheated steam at a pre-determined value.

References Cited in the file of this patent UNITED STATES PATENTS2,905,155 Grossman Sept. 22, 1959 2 ,947,289 Miller Aug. 2, 1960 FOREIGNPATENTS 1,135,874 France Dec. 22, 1956

